$re = '/(?<=, )[0-9]+(\.[0-9]+)?(?= fps)/';
$str = '8:9 DAR4:3], 23.98 fps
8:9 DAR4:3], 29.97 fps
8:9 DAR4:3], 25 fps
unrelated, 10 string
another, 28 fps string';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php